Spark-plug



1. M. HOFFMANN.

SPARK PLUG.4

APPLICATION FILED NOV. 4, 1919.

Patented Dec. 7, 1920.

Z 24527 l v f JOSEPH M. HOFFMANN, BROOKLYN, NEW YORK.

SPARK-PLUG.

Specification of Letters Patent.

Patented Dec. 7, 1920.

Application led November 4, 1919. Serial No. 335,604.

Z0 @ZZ whom it may concern.'

Be it known that'I, JosnrH'M. Horr- MANN, a citizen of the United States, residing at Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Spark- Plugs, of which the following is a full, clear, and exact specification.

This invention relates to spark plugs for internal combustion engines, and has for its object to provide a plug of simple construction and in which the parts may be readily assembled and retained in proper relative positions.

Another object is to produce a spark plug in which the upper electrode may be easily adjusted with respect to the lower electrode without disconnecting any of the parts of the device. It is also the aim of the invention to simplify the construction of the lower electrode and to prevent short circuiting between the upper electrode and the metallic casing of the plug.

v The invention will be first hereinafter de-y scribed in connection with the accompanying drawings, which constitute part of this specification, and then more specifically defined in the claims at the end of the description.

In the accompanying drawings, wherein similar reference-characters are used to designate corresponding parts throughout the v Fig. 4 is a section on the line IV-IV of Fig. 1, and

Fig. 5 is a view similar to Fig. 1 of a modified form of the invention. Referring first to Figs. 1 to 4, inclusive, of the drawin s, 1 `designates a metallic casing of the p ug having an upwardly .ta-

l pering conical bore 2, and 3 is a superlmposed body member of insulating material which is also provided with a conical bore 4 forming a continuation of the bore 2 in .the metallic casing 1. As shown in Figs. 1 and ,42, said body member 3 is composed of laminated sheets of mica. v

Fitted in the bores 2 and 4 of the casing 1 and body member 3, respectively, is a conical tubular insulating member 5 also preferably made of mica and extending entirely through to the bottom surface of said caslng. Said conical tubular member 5 is `clamped in place in the bores 2 and 4 by a the mica body member 3 for clampingjthe mica cone in place and' coupling the mica body member and metallic casing together.

The conical lmember 6 has a cylindrical bore 9 through which the upper electrode 10 loosely extends, but the lower end portionl of said bore is restricted and internally screw threaded at 11 to engagel external screw threads12 on the lower portion of said electrodel 10, whereby said electrode may be adjusted up and down by simply rotating the same in said conical member 6 after the latter has lbeen clamped'in place as above explained. The electrode 10 is clamped in adjusted position by a lock nut 13 threadedly engaging the threaded upper end portion 14 of said electrode and bearing against the n ut 8. The circuit wire 15 is clamped between the nut 13 and a binding nut 16 also threaded on the upper end of the electrode. l

The lower end of the electrode 10 is reduced to form an annular ledge or Step portion 17 a short distance above its lower extremity, and said lower extremity is formed with a substantially semi-spherical cavity 18V leaving a circular knife edge 19 from which the spark will jump to a rounded headed knob 20 on the lower electrode which consists of a U-shaped member 21 having its arms fixed in the metallic casing 1 so as to extend diametrically across the bore therein and position said knob 20 directly below the lower end of the upper electrode. The formation of the electrodes as shown and described with a circular knife edge opposite a rounded knob leaves no place for carbon to lodge and cause faulty sparking as is so often the case with many of the spark plugs as now generally in use. Should the ioo circular edge 19 become coated with carbon after long use, the ledge 17 will come into use as a sparking point and thus render the plug useful for a considerably longer time, the spark then jumping from said ledge 17 to the knob 20 over the carbon deposit on the circular edge 19.

The knob 2O is preferably formed on the cross bar of the lower electrode 21 by a punch and die (not shown) by which the middle portion of said cross bar is spread out and given a concavo-convex knob formation with a cavity 22 below it formed by the punch. rIhis manner of forming the knob reduces the cost of manufacture thereof to a minimum.

Referring to the modified form of the invention illustrated in Fig. 5, the metallic casing 23 is made like the casing l of the preferred form, and the upper and lower electrodes 24 and 25, respectively are also made like the corresponding parts in the preferred form. The insulating body mem ber 26, however, is made of a single piece of porcelain instead of the laminated sheets of mica in the preferred form, and said porcelain body member is capped by metallic plates 27 and 28 at the top and bottom, said plates having flanges 29 to protect the edges of the porcelain. In the modified form the conical clamping member 30 which is arranged in the tubular mica sleeve 3l does not extend above the porcelain body member, but is held in place to clamp said sleeve in the bores of the metallic casing 23 and porcelain body member by the nut 32 on the upper end portion of the upper electrode 242 which nut engages the upper plate 27, the clamping member 30 being adjustably engaged with the lower threaded end portion of said. electrode 24. The circuit wire 33 is clamped between the nut 32 and a binding nut 3e also threaded on the upper end of the electrode 24.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States isz- 1. In a spark plug, the combination with a metallic casing and a body member of insul-ating material having tapered bores in line with one another, of a conical sleeve of insulating material extending through the bores 0f both parts, a tubular` clamping member having a conical outer portion arranged in said sleeve and an externally threaded end portion extending above the body member, a nut on said threaded end portion of the clamping member t0 engage the upper end of the body member for holding the' sleeve in place and the metallic casing and body member together, and an electrode extending through said clamping member having its lower end portion screw threaded, the lower portion of said clamping member being internally threaded to engage the threads on the lower end of the electrode for axially adjusting the latter, and the upper portion of said electrode being spaced away from the bore of said clamping member.

2. In a spark plug, the combination with a metallic casing and a body member of insulating material having tapered bores in line with one another, of a conical sleeve of insulating material extending through the bores of both parts, a tubular clamping member having a conical outer portion arranged in said sleeve and having an externally threaded end portion extending above the body member, a nut on said threaded end portion of the clamping member to engage the upper end of the body member for holding the sleeve in place and the metallic casing and body member together, an electrode extending through said clamping member having its lower end portion screw threaded, the lower end portion of said member being internally threaded to engage said screw threads at the lower end of the electrode for axially adjusting the latter, and the upper portion of said electrode being spaced away from the bore of the clamping member, a lock nut on the upper end por- -tion of the electrode for engaging the first mentioned nut for retaining said electrode in adjusted position, and a wire binding nut to coperate with said lock nut for binding the circuit wire between them to said electrode. 3. In a spark plug, the combination with. a casing, of an upper electrode having a concave lower end with a sharp edge around it, and a lower electrode comprising a U- shaped member having its arms attached to said casing and a concavo-convex knob formed on said U-shaped member directly below the concave'lower end of the upper electrode.

4. In a spark plug, the combination with a casing, of an upper electrode having a concave lower end with a sharp edge around it, and a lower electrode comprising a U- shaped member having its .arms attached to said casing and a concavo-convex knob formed on said U-shaped member directly below the concave lower end of the upper electrode, said knob being of greater diameter than said concave lower end of the upper electrode.

In testimonj whereof I have signed my name to this specification.

JOSEPH M. HOFFMANN. 

